The invention concerns a process for the simultaneous production of methanol- and ammonia-synthesis gas from the crude gas of a coal gasification by H.sub.2 S-washing, conversion and CO.sub.2 washing of the crude gas, in which the condensed crude gas in connection with the H.sub.2 S-washing performed at low temperature is split into partial streams, which to different extents are subjected to further gas treatment.
The production of methanol- and/or ammonia-synthesis gas from so-called partial oxidation gas, that is gas, which has been obtained through gasification (partial oxidation) of solid or liquid fuel, has been known for a long time. Indeed according to the type of the therewith employed gasification processes, the gasification of the utilized fuel is performed at different pressures. One known gasification process operating in the low pressure range, that is between about 1 and 1.2 bar, is the Koppers-Totzek process. A particular advantage of this process is that it is useful for the gasification of any coal, independent of its degree of granulation and ash content. In so far as such a coal gasification process is supposed to be employed for the simultaneous production of methanol- and ammonia-synthesis gases, it was previously provided that the produced crude gas (partial oxidation gas), after its cooling in a waste-heat boiler and a direct water washing, initially be condensed in a so-called crude gas compressor up to a pressure of about 30 to 40 bar, and thereupon subsequently subjected to a H.sub.2 S-washing. For the H.sub.2 S-washing a so-called low temperature washing is particularly chosen, which operates with a suitable polar organic washing agent, such as for example methanol, in the temperature range between -20.degree. C. and -60.degree. C. In connection with the H.sub.2 S-washing, the gas is reheated and for purposes of adjusting the optimal composition of the methanol- and ammonia-synthesis gases, split into three partial streams, which to different extents are subjected to further gas treatments. Only the first partial stream is therewith subjected to not only a conversion but also a CO.sub.2 -washing, whereas the second partial stream is subjected to only a conversion. The third partial stream is, in contrast, subjected to neither a conversion nor a CO.sub.2 -washing. The so treated partial streams are subsequently reunited and introduced to the methanol synthesis or, after an additional liquid nitrogen washing, led into the ammonia synthesis.
With the methanol synthesis gas, it has however been shown herewith that the residual sulfur content of the partial stream of the gas, which was subjected only to the H.sub.2 S-washing, as well as the residual sulfur content of the partial stream which was subjected to the H.sub.2 S-washing and the conversion, are still too high. Since, however, the catalysts employed in the methanol synthesis are extraordinarily sulfur-sensitive, this leads in the long run to a considerable impairment of the methanol synthesis. It was therefore necessary to subject both of the previously mentioned partial streams of the gas before being reunited with the third partial stream to yet an additional treatment, a fine desulfurization, in which its residual sulfur content can be decreased to a value of about 0.1 ppm S. Normally, zinc oxide is employed as fine desulfurization mass. It is obvious that this fine desulfurization, not only in view of the apparatus, but also the operational costs, additionally burdens the processes for the production of methanol synthesis gas.
Previously, in normal fashion that partial stream of the gas was employed for the ammonia synthesis gas, which had run through all of the gas treatment stages. Accordingly, an additional fine desulfurization of the ammonia synthesis gas is as a rule not necessary.
The methanol synthesis gas produced by coal gasification contains inert gas components, essentially nitrogen, argon and methane, which must be excluded from the methanol synthesis. The gas excluded from the methanol synthesis is therewith normally designated as purge gas. It contains, in addition to the already mentioned inert gas component, also carbon dioxide as well as the valuable products hydrogen, methanol and carbon monoxide. Previously, this purge gas was either used as heating gas, or in additional apparatus the hydrogen was recovered from the purge gas. It is obvious that the purge gas is too valuable for combustion, and that the additional apparatus for the recovery of hydrogen from the purge gas additionally burdens not only the apparatus but also the operational costs of the entire process for the simultaneous production of methanol- and ammonia-synthesis gases.